This invention relates to an improved lubricating composition. More particularly, this invention relates to a lubricating composition having improved anti-oxidation and anti-wear properties.
It is highly advantageous to compound a lubricating oil so that it exhibits good anti-wear properties while at the same time having the ability to withstand oxidation over prolonged periods. The employment of anti-wear agents in lubricating oils, such as engine oils, transmission fluids, hydraulic fluids, etc., is well established. Numerous types of additives have been developed and several have proved quite successful in reducing wear and increasing equipment life. The conventional anti-wear agents which have experienced commercial success include the zinc dihydrocarbyl dithiophosphates, the zinc dialkyl dithiocarbamates, tricresyl phosphate, dilauryl phosphate, dialkyl phosphite, sulfurized terpenes, sulfurized sperm oil, various chlorinated compounds, etc. Of the above compounds, the zinc dihydrocarbyl dithiophosphates have essentially dominated the field.
While the conventional anti-wear agents have performed satisfactorily in the older equipment, the introduction of more powerful and high-speed machines has encouraged the development of anti-wear agents capable of imparting sustained anti-wear properties under elevated temperature conditions. The employment of zinc dihydrocarbyl dithiophosphates or other metal-containing anti-wear agents has not been entirely successful in these engines, since such agents are burdened with a high ash content. Some of the problems with the nonmetal-containing agents include the diminution of raw materials employed to produce some of the additives, i.e., reduction of availability of sperm whale oil, etc.
Thus, there has been a need for the development of an anti-wear agent having good anti-wear properties and not having a high ash content and that is relatively inexpensive to make.
In addition to the anti-wear properties, it is an important feature that the anti-wear agents be stable under an oxidizing environment. For example, the internal combustion engine is a model oxidator since it contacts a hydrocarbon motor oil with air under agitation and at high temperatures. Moreover, many of the metals manufactured into the engine and in contact with both the oil and air are excellent oxidation catalysts and effectively increase the rate of oxidation. The oxidation produces acidic bodies within the motor oil which are corrosive to typical bearings and additionally contributes to piston ring sticking, formation of sludges within the motor oil and over-all breakdown of the viscosity characteristics of the lubricant.
Several effective additives have been developed for imparting anti-oxidation properties to a lubricant. Their employment has been utilized in almost all of the conventional motor oils today. Typical of these inhibitors are the phenolic and thiophenolic anti-oxidants, such as the sterically hindered phenols and thiophenols, hindered hydroxy or thiolbenzoic acid esters, etc., aromatic amine anti-oxidants, such as alkylated phenyl amines, alkylphenyl-formaldehyde-amine polycondensates, etc., and the sulfurized oil-soluble organic compounds such as the sulfurized esters, sulfurized olefins, etc. Although these additives exhibit good anti-oxidation properties, many are often burdened with high costs when employed at the concentration necessary to impart the proper degree of oxidation inhibition, and others simply do not provide the desired degree of oxidation inhibition. Thus a need exists for an improved anti-oxidant that is stable at elevated temperatures, that can be employed at reduced concentrations, that is economical and relatively easy to produce and that can be used in combination with an anti-wear agent.
It is therefore an object of this invention to provide an improved lubricating composition.
It is an additional object of this invention to provide a lubricant composition having improved anti-oxidation properties. It is an additional object of this invention to provide a lubricant having improved anti-wear and anti-oxidation properties. Other additional objects will become apparent from the following description of the invention and the accompanying claims.